Method of preparing nanosized spherical vanadium oxide particle

ABSTRACT

A method of preparing nanosized spherical vanadium oxide particles, comprising preparing a vanadium ion-containing aqueous solution by dissolving a vanadium ion-containing material; adding at least one solvent selected from a non-protonic, polar organic solvent and a glycol solvent to the vanadium ion-containing aqueous solution and mixing the same; and aging the mixture.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of preparing nanosizedspherical vanadium oxide particles and, more particularly, to a methodof preparing nanosized spherical vanadium oxide particles having anaverage particle size of tens of nanometers using a sol-gel method.

[0003] 2. Description of the Related Art

[0004] Divanadium pentaoxide (V₂O₅) particles are generally preparedusing a solid phase method, a liquid phase method, or a vapor phasemethod. In the solid phase method, divanadium pentaoxide particles arederived from thermal decomposition of ammonium vanadate at a temperatureof 400-600° C. This solid phase method is relatively easy to perform,but the resulting divanadium pentaoxide particles have irregular shapesand large particle size on the order of several micrometers.

[0005] When divanadium pentaoxide particles are prepared using theliquid phase method, there is an advantage of easy processing withefficient control of particle size, crystal phase, and specific surfacearea. However, the resulting divanadium pentaoxide particles are limitedto planar or ribbon shapes, and thus spherical particles cannot beobtained using the liquid phase method.

[0006] The vapor phase method is divided according to the type of energysource, i.e., whether laser or plasma is used as an energy source. Inpreparing divanadium pentaoxide particles, the vapor phase method isdifficult to control and is less economical than the liquid phase andsolid phase methods.

[0007] Recently, there has been an increased interest in using nanosizedparticles in the development of new functional materials to improve theproperties of existing active materials as well as to obtain newproperties.

[0008] As electronic components have become smaller with increasedperformance requirements, the size of raw material particles forelectronic components has also decreased to the order of submicrons orless. For a uniform and fine distribution of sintering additiveparticles in a green body, there is a need to reduce the size of thesintering additive particles to a fine level. Reportedly, performance ofa sensor is improved by reducing the size of source particles with theeffect of increasing active surface area.

[0009] Divanadium pentaoxide particles have great electrochemicalactivity. Thus, divanadium pentaoxide particles are used as catalysts,electrochromic devices, anti-static coating materials, and activematerials for sensors and secondary cells. Discharge capacity of asecondary cell can be improved by using a nanosized, ribbon-shapedactive material, compared to a secondary cell manufactured using amicrosized active material. In additon to the application as activematerials for secondary cells, nanosized divanadium pentaoxide particlesare expected to show improved performance in applications of catalysts,electrochromic devices, anti-static coating materials, and activematerials for sensors. In the above and other applications, sphericalparticles are needed for better mixing, dispersion, or formingprocesses. Accordingly, for commercial applications of nanosizeddivanadium pentaoxide particles, there exists a need for an economic andefficient method for preparing nanosized divanadium pentaoxideparticles.

[0010] Up to now, however, an economic and efficient method of preparingnanosized divanadium pentaoxide particles having a spherical shape hasnot been developed.

SUMMARY OF THE INVENTION

[0011] According to a primary feature of the present invention, a methodof preparing nanosized spherical divanadium pentaoxide particlescomprises, preparing a vanadium ion-containing aqueous solution bydissolving a vanadium ion-containing material; adding at least onesolvent selected from a non-protonic, polar organic solvent and a glycolsolvent to the vanadium ion-containing aqueous solution and mixing thesame; and aging the mixture.

[0012] In preparing the vanadium ion-containing aqueous solution, thevanadium ion-containing material is dissolved in a hydrogen peroxideaqueous solution or an acid aqueous solution. Although the type of theacid aqueous solution that may be used is not limited, a hydrochloricacid aqueous solution, a nitric acid aqueous solution, or a sulfuricacid aqueous solution is preferred.

[0013] Preferably, the amount of hydrogen peroxide in the hydrogenperoxide aqueous solution or the amount of acid in the acid aqueoussolution is in the range of about 0.5 to 5 times the amount of vanadiumion-containing material in order to fully dissolve the vanadiumion-containing material. If the amount of hydrogen peroxide or theamount of acid exceeds the above stated range, it becomes uneconomicaldue to a relative low concentration of vanadium ions. If the amount ofhydrogen peroxide or the amount of acid is less than the above statedrange, it becomes difficult to fully dissolve the vanadiumion-containing material.

[0014] Preferably, the vanadium ion-containing aqueous solution containsbetween about 0.01 to 0.5 M vanadium ion.

[0015] In accordance with a preferred embodiment of the presentinvention, the non-protonic, polar organic solvent is at least oneselected from the group consisting of N-methyl-2-pyrrolidone,N,N-dimethylacetamide, hexamethylphosphoamide, and pyridine, and theglycol solvent comprises at least one selected from the group consistingof ethyleneglycol, propyleneglycol, and butyleneglycol. The amount ofthe solvent is in a preferred range of about 60-98% by volume based onthe total volume of the vanadium ion-containing aqueous solution and thesolvent.

[0016] Aging of the mixture is performed preferably for about 0.5 to 100hours at a temperature not less than 0° C. and not greater than thehigher of the boiling point of the vanadium ion-containing aqueoussolution and the boiling point of the solvent.

[0017] In the method for preparing vanadium oxide particles according tothe present invention, any vanadium ion-containing material can be usedwithout limitations, but divanadium pentaoxide is preferred.

[0018] These and other features and aspects of the present inventionwill be readily apparent to those of ordinary skill in the art uponreview of the detailed description that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The above features and advantages of the present invention willbecome more apparent by describing in detail preferred embodimentsthereof with reference to the attached drawings in which:

[0020]FIG. 1 is a scanning electron microscopic (SEM) photograph ofdivanadium pentaoxide (V₂O₅) particles prepared in Example 1 inaccordance with the present invention;

[0021]FIG. 2 is a graph illustrating an X-ray diffraction pattern ofdivanadium pentaoxide particles prepared in Example 1 in accordance withthe present invention;

[0022]FIG. 3 is a SEM photograph of divanadium pentaoxide particlesprepared in Example 5 in accordance with the present invention;

[0023]FIG. 4 is a SEM photograph of divanadium pentaoxide particlesprepared in Example 6 in accordance with the present invention;

[0024]FIG. 5 is a SEM photograph of divanadium pentaoxide particlesprepared in Example 7 in accordance with the present invention;

[0025]FIG. 6 is a SEM photograph of divanadium pentaoxide particlesprepared in Example 8 in accordance with the present invention;

[0026]FIG. 7 is a SEM photograph of divanadium pentaoxide particlesprepared in Comparative Example 1; and

[0027]FIG. 8 is a graph illustrating an X-ray diffraction pattern ofdivanadium pentaoxide particles prepared in Comparative Example 1.

DETAILED DESCRIPTION OF THE INVENTION

[0028] Korean Patent Application No. 2001-16325 filed Mar. 28, 2001, andentitled “Method of Preparing Nanosized Spherical Vanadium OxideParticle,” and Korean Patent Application No. 2001-73735, filed Nov. 26,2001, and entitled “Method of Preparing Nanosized Sperical VanadiumOxide Particle,” are incorporated by reference herein in their entirety.

[0029] In a sol-gel method, formation of particles involves nucleationthrough hydrolysis and condensation and growth of the nuclei. The shape,particle size, and particle size distribution of the resulting particlesare affected by reaction factors and conditions during nucleation andgrowth. Therefore, adjustment of the reaction conditions and factors isrequired to form particles having a desired shape, particle size, andparticle size distribution.

[0030] It is known that formation of particles having a particularorientation on a crystal plane using the sol-gel method is greatlyaffected by growth. When a particular oriented crystal plane of amaterial has the lowest surface energy in a reaction solvent among othercrystal planes in the growth step, the particular oriented crystal planegrows first to reduce the system energy such that growth of othercrystal planes is suppressed. The resulting particles are surrounded bythe particular oriented crystal plane having the lowest surface energyin the reaction solvent so that they have a non-spherical shape. Incontrast, when all the crystal planes of a material have the samesurface energy in a reaction solvent, nuclei growth occurs in everydirection, and the resulting particles having a spherical shape.Therefore, to form spherical divanadium pentaoxide particles using aliquid phase method including a sol-gel method, the surface energy ofall crystal planes of divanadium pentaoxide in a reaction solvent shouldbe equal.

[0031] The surface energy of an oriented crystal plane of a material ina reaction solvent can be varied by adsorbing a surfactant to theoriented crystal plane or by changing the reaction solvent.

[0032] In the present invention, a mixed solvent of water and anon-protonic, polar organic solvent and/or a mixed solvent of water andglycol are used as the reaction solvent to obtain nanosized sphericaldivanadium pentaoxide particles. Suitable non-protonic, polar organicsolvents include N-methyl-2-pyrrolidone, N,N-dimethylacetamide,hexamethylphosphoamide, pyridine, and mixtures of these solvents.Suitable glycols include ethyleneglycol, propyleneglycol,butyleneglycol, and mixtures of these materials. The amount of thereaction solvent is in a preferred range of about 60 to 98% by volumebased on the total volume of a vanadium ion-containing aqueous solutionand the reaction solvent.

[0033] A method of preparing nanosized spherical divanadium pentaoxideparticles using a sol-gel method according to the present invention willnow be described below.

[0034] First, a vanadium ion-containing aqueous solution is prepared bydissolving a vanadium ion-containing material in an aqueous solution.When divanadium pentaoxide is used as the vanadium ion-containingaqueous material, the vanadium ion-containing aqueous solution isprepared by dissolving divanadium pentaoxide in a hydrogen peroxideaqueous solution or an acid aqueous solution such as a hydrochloric acidaqueous solution, a nitric acid aqueous solution, or a sulfuric acidaqueous solution. Preferably, the vanadium ion-containing aqueoussolution is prepared by dissolving divanadium pentaoxide in the hydrogenperoxide aqueous solution. Benefits of using the hydrogen peroxideaqueous solution include ease of use without residual ions.

[0035] Although the concentrations of the hydrogen peroxide aqueoussolution and the acid aqueous solution are not limited, it is preferredthat the concentration of the hydrogen peroxide aqueous solution is 30%,30 to 32%, 35%, or 50% by weight, while it is preferred that theconcentration of the acid aqueous solution is 20%, 37%, or 38% by weightfor the hydrochloric acid aqueous solution, 70% or 90% by weight for thenitric acid aqueous solution, and 95 to 98% or 98% by weight for thesulfuric acid aqueous solution.

[0036] Preferably, the vanadium ion-containing aqueous solution containsabout 0.01M to 0.5M vanadium ion. If the concentration of the vanadiumion is less than 0.01M, it is undesirable for economical reasons. If theconcentration of the vanadium ion exceeds 0.5M, it is undesirable forthe shape of divanadium pentaoxide particles in the vanadiumion-containing aqueous solution.

[0037] The prepared vanadium ion-containing aqueous solution is mixedwith a non-protonic, polar organic solvent and/or a glycol solvent.Suitable non-protonic, polar organic solvents includeN-methyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoamide,pyridine, and mixtures of these solvents. Suitable glycol solventsinclude ethyleneglycol, propyleneglycol, butyleneglycol, and mixtures ofthese materials.

[0038] The amount of the solvent is in a preferred range of 60-98% byvolume based on the total volume of the vanadium ion-containing aqueoussolution and the solvent. If the amount of the solvent is less than 60%by volume, it is undesirable from the standpoint of the shape of theresulting divanadium pentaoxide particles. If the amount of the solventexceeds 98% by volume, it is uneconomical because of a too low of avanadium ion concentration.

[0039] Next, the mixture of the vanadium ion-containing aqueous solutionand the non-protonic, polar organic solvent, the mixture of the vanadiumion-containing aqueous solution and the glycol solvent, or the mixtureof the vanadium ion-containing aqueous solution, the non-protonic, polarorganic solvent, and the glycol solvent is aged at a temperature,preferably no less than 0° C. and no greater than the higher of theboiling point of the vanadium ion aqueous solution and the boiling pointof the solvent. Preferably, aging is performed for 0.5-100 hours. If theaging time is less than 0.5 hours, divanadium pentaoxide particlescannot be formed. If the aging time exceeds 100 hours, it is undesirablefor economical reasons. If the aging temperature is less than 0° C., thereaction rate is too slow or the divanadium pentaoxide generationreaction itself does not occur. If the aging temperature exceeds theupper limit, an additional hydrothermal reactor is needed to suppressexcess evaporation of the solvent or water from the reaction mixture.

[0040] After the aging is completed, precipitates are filtered from thereaction product and dried to obtain divanadium pentaoxide particlesaccording to the present invention.

[0041] According to the preparation method described above, sphericaldivanadium pentaoxide particles having an average particle size of tensof nanometers, and particularly 30-80 nm, can be prepared efficientlyand economically.

Example 1

[0042] 4.5728 g of cystalline divanadium pentaoxide (V₂O₅) granules(99.6% purity) was placed in a beaker containing 150 ml of distilledwater. 25 ml of 30% (by weight) hydrogen peroxide (H₂O₂) solution wasadded to the solution and thoroughly mixed to fully dissolve V₂O₅. Next,distilled water was added making the total volume of the reaction mixure200 ml to prepare a vanadium ion-containing aqueous solution containing0.5M vanadium ion.

[0043] 40 ml of the vanadium ion-containing aqueous solution was addedinto a reaction container containing 160 ml of N-methyl-2-pyrrolidoneand mixed. The reaction container was plugged and aged for 12 hours in athermostatic bath at 80° C.

[0044] After aging, precipitants were filtered from the reaction productand dried in a dry chamber at 60° C. to prepare divanadium pentaoxideparticles.

[0045] A scanning electron microscopic (SEM) photograph and a graphillustrating an X-ray diffraction pattern for the divanadium pentaoxideparticles prepared in Example 1 are shown in FIGS. 1 and 2,respectively. FIG. 1 shows that the divanadium pentaoxide particlesprepared in Example 1 are spherical with an average particle size ofabout 40 nm. The result of the X-ray diffraction analysis illustrated inFIG. 2 shows that the divanadium pentaoxide particles prepared inExample 1 are amorphous.

[0046] A vanadium-to-oxygen ratio was measured for the divanadiumpentaoxide particles prepared in Example 1 using an inductively coupledplasma emission spectrometer. The divanadium pentaoxide particlesprepared in Example 1 had a vanadium-oxygen ratio of 2:5 by mole.

Example 2

[0047] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that the concentration of vanadium ion was 0.2M.Physical properties of the divanadium pentaoxide particles weredetermined. As a result, the divanadium pentaoxide particles prepared inExample 2 were spherical and amorphous and had an average particle sizeof about 40 nm.

Example 3

[0048] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that the concentration of vanadium ion was 0.1M. Physical properties of the divanadium pentaoxide particles weredetermined. As a result, the divanadium pentaoxide particles prepared inExample 3 were spherical and amorphous and had an average particle sizeof about 35 nm.

Example 4

[0049] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that the concentration of vanadium ion was 0.01M. Physical properties of the divanadium pentaoxide particles weredetermined. As a result, the divanadium pentaoxide particles prepared inExample 4 were spherical and amorphous and had an average particle sizeof about 30 nm.

Example 5

[0050] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that N,N-dimethylacetamide instead ofN-methyl-2-pyrrolidone was used. Physical properties of the divanadiumpentaoxide particles were determined. A SEM photograph of the divanadiumpentaoxide particles prepared in Example 5 is shown in FIG. 3. As shownin FIG. 3, the divanadium pentaoxide particles prepared in Example 5were spherical and crystalline and had an average particle size of about80 nm.

Example 6

[0051] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that hexamethylphosphoamide instead ofN-methyl-2-pyrrolidone was used. A SEM photograph of the divanadiumpentaoxide particles prepared in Example 6 is shown in FIG. 4. As shownin FIG. 4, the divanadium pentaoxide particles prepared in Example 6were spherical and crystalline and had an average particle size of about40 nm.

Example 7

[0052] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that pyridine instead of N-methyl-2-pyrrolidonewas used. A SEM photograph of the divanadium pentaoxide particlesprepared in Example 7 is shown in FIG. 5. As shown in FIG. 5, thedivanadium pentaoxide particles prepared in Example 7 were spherical andhad an average particle size of about 40 nm. The divanadium pentaoxideparticles prepared in Example 7 also included 50% or less needle-shapedor rod shaped particles having an average diameter size of about 40 nm.

Example 8

[0053] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that ethyleneglycol instead ofN-methyl-2-pyrrolidone was used. A SEM photograph of the divanadiumpentaoxide particles prepared in Example 8 is shown in FIG. 6. As shownin FIG. 6, the divanadium pentaoxide particles prepared in Example 8were spherical and amorphous and had an average particle size of about80 nm.

Example 9

[0054] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that 4 ml of the vanadium ion-containingsolution and 196 ml of N-methyl-2-pyrrolidone were used. Physicalproperties of the divanadium pentaoxide particles were determined. As aresult, the divanadium pentaoxide particles prepared in Example 9 werespherical and amorphous and had an average particle size of about 30 nm.

Example 10

[0055] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that 60 ml of the vanadium ion-containingsolution and 140 ml of N-methyl-2-pyrrolidone were used. Physicalproperties of the divanadium pentaoxide particles were determined. As aresult, the divanadium pentaoxide particles prepared in Example 10 werespherical and amorphous and had an average particle size of about 40 nm.

Example 11

[0056] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that 80 ml of the vanadium ion-containingsolution and 120 ml of N-methyl-2-pyrrolidone were used. Physicalproperties of the divanadium pentaoxide particles were determined. As aresult, the divanadium pentaoxide particles prepared in Example 11 werespherical and amorphous and had an average particle size of about 40 nm.

Example 12

[0057] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that aging was performed at 20° C. Physicalproperties of the divanadium pentaoxide particles were determined. As aresult, the divanadium pentaoxide particles prepared in Example 12 werespherical and amorphous and had an average particle size of about 40 nm.

Example 13

[0058] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that 25 ml of 98% (by weight) sulfuric acidaqueous solution instead of 25 ml of 30% (by weight) H₂O₂ aqueoussolution was used. The physical properties of the divanadium pentaoxideparticles were determined. As a result, the divanadium pentaoxideparticles prepared in Example 13 were spherical and amorphous and had anaverage particle size of about 40 nm.

Example 14

[0059] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that propyleneglycol instead ofN-methyl-2-pyrrolidone was used. Physical properties of the divanadiumpentaoxide particles were determined. As a result, the divanadiumpentaoxide particles prepared in Example 14 were spherical and amorphouswith an average particle size of about 40 nm.

Comparative Example 1

[0060] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that water instead of the organic solvent(N-methyl-2-pyrrolidone) was used. Physical properties of the divanadiumpentaoxide particles were determined.

[0061] A SEM photograph and a graph illustrating an X-ray diffractionpattern for the divanadium pentaoxide particles prepared in ComparativeExample 1 are shown in FIGS. 7 and 8, respectively. FIG. 7 shows thatthe divanadium pentaoxide particles prepared in Comparative Example 1have a ribbon shape. The result of the X-ray diffraction analysisillustrated in FIG. 8 shows that the divanadium pentaoxide particlesprepared in Comparative Example 1 are crystalline.

Comparative Example 2

[0062] Divanadium pentaoxide particles were prepared in the same manneras in Example 1, except that aging was not performed. As a result, theparticle generation reaction did not occur.

[0063] The experimental conditions for the preparation of divanadiumpentaoxide particles in Examples 1 through 14 and Comparative Example 1and 2 are summarized in Table 1. The result of the physical propertydetermination for the divanadium pentaoxide particles prepared inExamples 1 through 14 and Comparative Examples 1 and 2 are summarized inTable 2. TABLE 1 Vanadium ion Amount of concentration Solvent (% byExample (M) Reaction Solvent volume) Aging Conditions Example 1 0.5N-methyl-2-pyrrolidone 80 80° C. for 12 hours Example 2 0.2N-methyl-2-pyrrolidone 80 80° C. for 12 hours Example 3 0.1N-methyl-2-pyrrolidone 80 80° C. for 12 hours Example 4 0.01N-methyl-2-pyrrolidone 80 80° C. for 12 hours Example 5 0.5N,N-dimethylacetamide 80 80° C. for 12 hours Example 6 0.5Hexamethylphosphoamide 80 80° C. for 12 hours Example 7 0.5 Pyridine 8080° C. for 12 hours Example 8 0.5 Ethyleneglycol 80 80° C. for 12 hoursExample 9 0.5 N-methyl-2-pyrrolidone 98 80° C. for 12 hours Example 100.5 N-methyl-2-pyrrolidone 70 80° C. for 12 hours Example 11 0.5N-methyl-2-pyrrolidone 60 80° C. for 12 hours Example 12 0.5N-methyl-2-pyrrolidone 80 20° C. for 12 hours Example 13 0.5N-methyl-2-pyrrolidone 80 80° C. for 12 hours Example 14 0.5Propyleneglycol 80 80° C. for 12 hours Comparative 0.5 H₂O 80 80° C. for12 hours Example 1 Comparative 0.5 N-methyl-2-pyrrolidone 80 No agingExample 2

[0064] TABLE 2 Average Particle Example Particle Shape Size (nm) CrystalPhase Example 1 Spherical 40 Amorphous Example 2 Spherical 40 AmorphousExample 3 Spherical 35 Amorphous Example 4 Spherical 30 AmorphousExample 5 Spherical 80 Crystalline Example 6 Spherical 40 CrystallineExample 7 Spherical and 50 Crystalline Needle-like Example 8 Spherical80 Amorphous Example 9 Spherical 30 Amorphous Example 10 Spherical 40Amorphous Example 11 Spherical 40 Amorphous Example 12 Spherical 40Amorphous Example 13 Spherical 40 Amorphous Example 14 Spherical 40Amorphous Comparative Ribbon-like — Crystalline Example 1 Comparative Noreaction Example 2

[0065] As shown in Table 2, spherical vanadium pentaoxide particleshaving an average particle size of 30-80 nm were prepared in Examples 1through 14. In contrast, divanadium pentaoxide particles prepared inComparative Example 1 using water instead of the organic solvent had aribbon shape. In Comparative Example 2 where aging was not performed,vanadium pertoxide particles could not be formed because no reactiontook place.

[0066] As described above, in the preparation of divanadium pentaoxideparticles by the sol-gel method according to the present invention, amixed solvent of water and a non-protonic, polar organic solvent or amixed solvent of water and a glycol are used as a reaction solvent sothat spherical divanadium pentaoxide particles having an averageparticle size of tens of nanometers can be prepared efficiently andeconomically.

[0067] While this invention has been particularly shown and describedwith reference to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A method of preparing vanadium oxide particles,comprising: (A) preparing a vanadium ion-containing aqueous solution bydissolving a vanadium ion-containing material; (B) adding at least onesolvent selected from a non-protonic, polar organic solvent and a glycolsolvent to the vanadium ion-containing aqueous solution and mixing thesame; and (C) aging the mixture.
 2. The method of preparing vanadiumoxide particles as claimed in claim 1, wherein, in step (B), thenon-protonic, polar organic solvent is at least one selected from thegroup consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide,hexamethylphosphoamide, and pyridine, and the glycol solvent comprisesat least one selected from the group consisting of ethyleneglycol,propyleneglycol, and butyleneglycol.
 3. The method of preparing vanadiumoxide particles as claimed in claim 1, wherein the amount of the solventis in the range of 60-98% by volume based on the total volume of thevanadium ion-containing aqueous solution and the solvent.
 4. The methodof preparing vanadium oxide particles as claimed in claim 1, wherein thevanadium ion-containing aqueous solution in step (A) contains vanadiumion in the range of 0.01-0.5 M.
 5. The method of preparing vanadiumoxide particles as claimed in claim 1, wherein, in step (A), thevanadium ion-containing material is dissolved in a hydrogen peroxideaqueous solution or an acid aqueous solution.
 6. The method of preparingvanadium oxide particles as claimed in claim 5, wherein the acid aqueoussolution is selected from the group consisting of hydrochloric acidaqueous solution, nitric acid aqueous solution, and sulfuric acidaqueous solution.
 7. The method of preparing vanadium oxide particles asclaimed in claim 5, wherein, in step (A), the amount of hydrogenperoxide in the hydrogen peroxide aqueous solution or the amount of theacid in the acid aqueous solution is in the range of 0.5-5 times thevanadium ion-containing material.
 8. The method of preparing vanadiumoxide particles as claimed in claim 1, wherein aging in step (C) isperformed for 0.5-100 hours at a temperature not less than 0° C. and notgreater than the higher of the boiling point of the vanadiumion-containing aqueous solution and the boiling point of the solvent.